I'm considering using my sawblades on my '87. I'm about 95% sure but wanted to confirm with the board. Are these correct ? (link below). Has anyone used them / any other suggestions ?

I emailed corvettemods with a few questions about the difference between these and other ones they sell (that also appear to be correct) that were a few dollars more. I've had my eyes open on the forum for a good used set with no luck.

(Corvette Mods "almost less than" 2 word reply was: ......... different mfgs ). (Very professional / detailed reply right ?? )

https://www.corvettemods.com/Aluminu...r_p_19443.html

Just looking for opinions. From the pics, they appear to be hubcentric etc.

 

Those will work fine. Hubcentricity doesn't even matter - it's just a convenience bonus. These adapters - like all wheels - will actually center on the studs. The only thing to watch for with this is that your studs on the car might poke through far enough that they hit the back of the wheel and prevent it from seating on the adapter. Some OE wheels have little pockets that prevent this problem. Just make sure when you mount them for the first time.

The alternative is to use a plain pass-through spacer. It's actually stronger and cheaper, but for 3/4" (which is what you should need) you would need to replace your wheel studs with longer ones. I understand that for 84-87 C4s that is a pain to do on the rear hubs. These adapters are a lot easier.

 

I agree with you. I always look for hubcentric if possible the last few times I've used adapters. Like you said, just for convenience sake. The sawblades have those pockets as well, so that's nice that you don't have to worry about the studs hitting the rims. (The stock rims anyway, I've seen a few aftermarket rims cause some issues in the past).

I used the "regular spacers" on my 72 Mustang Vert, and like you said, I installed the longer studs. For 3/4" I think the adapters are just fine.

thanks for the reply. I figured those would be correct..

 

The only thing other than what's been mentioned that 'would/might' concern me. We've actually 'pinned' a couple sets of these adapters so as to avoid spinning a stud in the adapter. None of these were mine but the knurl on the studs is an unknown as to fit, length of knurl etc. The fellow that we pinned first actually experienced the issue. He mentioned it was enough of an issue he didn't mind spending the $$$ so as to avoid it with his next purchase. He didn't quit the use of 'adapter styled spacer' but if the vendor wouldn't pass on to him the actual specs of the stud regarding knurl diameter and length he bought elsewhere.

Does "different manufacturer" fit the vendor he left behind? Guess!!

Is there a particular reason you've limited yourself to the 3/4"/19mm spec?

 

Since I was using the stock sawblades, it "seemed" the consensus was that most were using 3/4" / 20mm adapters. I did see a few posts on various forums showing people using 1" and 1.25" adapters but one car I looked at in person (1" adapters) "seemed to me" to have the rims pushed out "to about the maximum amount" . While the rim and tread were not "sticking past the body", the tire "sidewall bulge" seemed to be slightly past the body of the car (at least in my eyes) and looked off to me. Of course, that could have been the tire design itself.

Before, I always thought the 1" would be perfect for the 9.5" 56mm sawblades but the 2nd car I saw with the 3/4" looked perfect to me. I guess it's possible that the first car I saw had 1.25" and not 1" (although the owner was sure they were 1"). Both cars I looked at were running the stock 275's on all 4's, so for that reason, I thought the 3/4" was what to go with. (I'm a C3 guy, and had 3 C4's over the years, but I'm not as familiar with them).

That's an excellent point though about the knurl.
I admit, I did not think of that in respect to a 3/4" spacer. I have not heard of anyone spinning the studs, but could very well see that happening.

Are others using 1" with stock sawblades ? I'm not married to 3/4" that for sure...

Thanks for the insight.. Now you have me thinking. I have not ordered yet.

A few have mentioned that they were happy with these from European Motorwerks. Any thoughts??

https://www.ebay.com/itm/4-20mm-5x4-...item42078a4d2b

I'm guessing they make a 1" as well. which my be an option.

 

To correct your specs, a stock 17x9.5 sawblade has an offset of 56mm, not 65. A 16x9.6 turbine from the 87 had 38mm offset. So there's an 18mm difference, and a 3/4" spacer is about 19mm. That spacer will sit the sawblades 1mm further out than the stock turbines (i.e. they are basically in the same place).

Your fenders will easily accommodate a 1" spacer with the sawblades if you like the wider look. 1.25" is getting very close to flush with the outer fender edge, and 1.5" will either have the edge of the tread blocks flush or a touch outside (depending on tire model and camber setting) and the sidewall bulge will be outside the fender edge. The further outside you put the centerline of the tread, the more load you put on the wheel bearings. I honestly don't know how big a deal that is to their longevity. You also increase scrub radius, which on your car is already greater than on later cars. That might add a little weirdness to the steering feel and increase the tendency to tramline. I'm not sure that's a very big deal either, even with the 1.25" adapters. Those are the potential downsides to going with more then 3/4" adapters, but I don't see either of them as deal breakers if you want to push the sawblades further out than stock.

 

Thanks for noticing that. I mistyped. I'm aware they are 56mm. Corrected in my last post.

Now I'm wondering if I should just get the 1" adapters. (I'm actually just installing the sawblades for the look. Although I do like the turbines, (mine are in pristine shape), the tire choices for 16" are pretty slim now. So I'm just looking for something to allow me to mount the rims correctly as opposed to going for a wide-track look / performance etc. As long as they are not sticking out, I'm happy ... I wish I could track a car down using the 1" spacers and sawblades to get an idea of how "they sit".

When doing the math, I came out with the same 1mm difference as you did and figured that the 3/4" was the way to go. (Although some of the 3/4" spacers are listed as 3/4" / 20mm which isn't really correct. I guess they round up from 19.05mm. Although, how critical can you be when you're talking about 1mm ! ) Hmmmmmm now I'm second guessing the 3/4's ... after the knurling comment above !

 

I disagree on hubcentricity. The hub center is there to center the wheel. Bolts are to clamp the wheel in place. The clamping force create friction between hub and wheel to transfer torque. The bolts should not transfer torque. That is the reason why you should not apply any grease on the hub face, only on threads.
Bolts does not center the wheel very well. You could use BMW wheels on a Chevrolet. ( a lot of people do ) BMW use 5x120 mm and Chevrolet use 5x4.75 inch = 5x120.65 mm. That is over 0.3 mm offset on each bolt. About 1/64 inch.

There are also lug centric wheels.

Using a thin spacer you often hide the hub center and the wheel might not center as it should.
In this case a hubcentric adapter is better if it is matched to both hub and wheel. But it needs some thickness to have place for bolts and also be stiff enough.

It is the same process to replace wheel studs on the hub as on the later Corvettes, as the use the same hub. It is a bit more work to get the hub out because of the drum style parking brake.

 

I agree with everything in that video except the statement that on lugcentric mountings the torque of the lug nuts locates the wheel. It's not the torque that locates the wheel - it's the centering force applied by the tapered lug nut and seat.
The lug nuts don't transfer torque. They apply a tension force to the studs. You are correct that the clamping force created by that tension is what hold the wheel in place.

According to whom do the studs and nuts not center wheels very well? Even the video you linked specifically shows that lug centering works just fine. And no, you should not use 5x120mm wheels on a 5x4.74" hub. It's improper fitment and will create a bending force on the studs. It will also wallow out the tapered seats in the wheels over time.

There have been hundreds of millions of vehicles sold brand new without hubcentric hubs and wheels. This includes race-specific applications. They work fine. If you have a hubcentric design and the studs don't "agree" with the hub's location of the wheel, then you have problems with either a poorly manufactured hub or bent studs. Assuming that's not an issue, then the studs and hub will locate the wheel in the exact same place.

Agreed, it's the parking brake differences I was referring to. I've just never done the job on an earlier Corvette and therefore wasn't sure how much extra work that adds to the job.

 

Great comments above. For something like an adapter I personally think hubcentric is the way to go. That's why I personally prefer a hubcentric adapter over a pass through spacer (on a car / wheel that is currently hubcentric since (as mentioned) the spacer effectively eliminates that). I've had plenty of old cars where the rim hub bore was substantially larger than the hub (especially on old mag wheels and some steel wheels) and as mentioned above, millions of cars were produced that way and were just fine.

I think as "technology advances" and things change and improve, things like a hubcentric design is a no brainer if the option is there. (But not necessary). I've had quite number of Unilug rims that fit my old Mustangs for example as well as the Dodge / Chrysler bolt pattern. I still have a set of unilug Crager SS rims in the basement. The lug holes were so oblong and the only thing centering the rims was the long lug that passed through the hole (usually a integrated or separate washer for the lug nut was used as well). Some of those rims had a 2.5" center hole that "eclipsed" the size of the hub , and they stayed mounted just fine.

I know the 5x4.75 compared to 5x120 debate has been going on for quite sometime. (I have a 1998 BMW 540 and am familiar with those rims as well). My general belief is that you don't "use things" that are not designed for a particular application. I too have seen numerous Chevy's and GM cars running BMW rims. My personal feeling is that I would stick with proper rims for the car, BUT I do also believe that the differences in 4.75 vs 120 is extremely miniscule . Although I wouldn't use my BMW rims on my Corvette or any other GM car, I can see that most likely there wouldn't be issues.

Someone on the Thridgen forum that I belong to as well., did pretty good visual comparison awhile back. I thought it was interesting.

https://www.thirdgen.org/forums/whee...-vs-5x120.html

P.S. Does anyone remember those old Appliance rims with the Roto-lug eccentric lug nuts? Those things never seem to stay balanced for me! On the surface, not a fantastic idea, but people are still using them with no issues. Some info / instructions for them at this thread.

https://www.opelgt.com/threads/appli...shings.104378/

 

For what it's worth I agree with Joby here. I put some aftermarket Epsilon 3 piece wheels on a Porsche I used to have. The wheels had a larger centre bore so weren't hubcentric anymore and I got some vibration at higher speed. I tried retorquing the wheel nuts a few time but then had some spigot rings machined to fit and this solved my issue. I would always look for hubcentric spacers since the cost is similar.

 

There C4 corvette is designed with hub centric wheels.
Usually the manufacturing tolerances are good so studs and holes in the rim are also in the correct position.
When using stock wheels the first nut and hub center will locate the wheel. You should of course tighten nuts in a star pattern anyway.
If using non stock rims, or spaces, so hub center is not used. It is much more important to snug up the nuts in a star pattern and make sure that the rim is not 'hanging' when tightening nuts.
Without hub center it is very possible to torque the wheel in place off center, especially if you are not aware of the potential problem.

When torqued down it does not matter as the rim will not move on the hub. If you don't have any vibrations then all is good.

 

In all my decades of installing wheels - often weekly for competitions - I have never encountered this. Not once. This is despite the fact that many times the wheels I used were not hubcentric. The same is true of all the steel wheels used by NASCAR stock cars: they are certainly not careful to follow a star pattern in their pit stops and don't even worry about a specific torque value! They run those lug nuts on in a circular pattern to whatever torque values their hopped up impact wrenches end up at, as fast as they can (1-2 seconds for all five!), and send it. And yet somehow they remain vibration-free at over 200mph...every single time.

That said, I agree with using a star pattern and proper lug nut torque, but that has way more to do with preserving the wheels/hubs/studs than locating the wheel. What I don't agree with is making statements that are not borne out by facts/proof. It simply is not "very possible" to torque a lugcentric wheel off center unless there is something wrong with the wheel's lug nut seats or the wheel studs (even then, it's pretty hard to mess it up if the problem is just one seat or stud). Again, if it were possible than the wheel balancing you showed would be wrong because it wouldn't be possible to reliably balance a lugcentric wheel.

Once you get to 1/2" pass-through spacers or thicker, you can get those with hubcentric designs just like adapters (I think adapters can't reliably be made thinner than 3/4", though).

 

I think you're correct. I don't think less than 3/4" is enough material to allow studs to be inserted. Well...... I'm sure they can be inserted...... but how long they stay in there before the adapter grenades itself in use is another story... !

 

Can someone tell me why a spacer like this one.... :

https://www.corvettemods.com/C3-C4-C...r_p_15636.html

.... has a 70.5 Center Bore and not 70.3mm. I realize the difference is like a human hair, but the reason why I ask: I figured I'd go with the Hubcentric, blah, blah , blah.

So the adapter fits on the hub of my '87 (Which all measure 70.1 / 70.2mm) and just slides right on. (There is some play, not as "tight" as the rim fits that's for sure). Is this difference "normal" / expected? I realize there my be small differences on some of these tolerances, but wanted to be sure these are ok to use. The lug nuts certainly "center it up", but it's not as tight of a fit as a factory rim mounted to the hub. I personally thought they would be a "tighter fit". It's funny how you can feel .2mm or so..

Next. (The reason why these DON'T seem to work on my Factory Sawblades: The Hubcentric portion of the adapter is also 70.5mm and my rims are 70.3mm so the rim will not "seat" on this adapter. (Rims are clean, no corrosion etc).

This morning so far, I've tried: (2) 1984 Rims, (1) 1986 Rim, (2) 1987 Rims, (2) 1992 Rims (ALL Factory C4). The hub diameter of all of those rims range from 70.1 - 70.4mm - sooooo NONE of those rims will fit over the 70.5 mm hubcentric portion of the spacers.

Why would these be 70.5MM ? (I can possibly see where the back portion of the spacer that contacts the hub may be slightly larger to allow for possible mfg differences in the hubs (??), but why on earth would the portion that the rim slips over be 70.5, when I can't find stock c4 rim I have here with a hub bore over 70.4mm? (with the majority of them being 70.1 and 70.2mm) ??

Seems Odd.

 

I did some calculations, and if I am correct ... Moving the tire center 0.2 mm would require the smallest wheel weight to compensate unbalance.

So anything less off center falls within the tire balancing accuracy.

 

That's a good question. If you look on wheel-size.com, all Corvettes at least from C3-C7 have a center bore of 70.3". So if the Corvette Mods adapters are 70.5", then they are out of spec. There are other cars out there with a 70.5" bore, but not any Corvettes I can find. Time to send those back for a refund. A super-quick Google scan shows plenty of 20mm adapters out there with the correct center bore diameter, so there is no sense in fooling around with these.

 

It seems OP got exactly what was 'ordered' and assuming OP reviewed the 'advertised' specifications should have known better. These weren't advertised to be OE specs anywhere. OP questioned the 'two word' response to his first question to the vendor. Might the OP have considered a question this time around?

***Majority of after-market wheels have a 'center-bore' that is by spec greater than OE. It appears that for the majority of their wheel offerings 'center-bore' isn't even mentioned. The vendors reputation in the past in particularly the C4 section has always been less than 'spectacular'

.Except when it DOES I do realize I've maybe 'stretched' the specific definition but when shopping spacer/adapter 'centricity' should likely always be considered.

-------------------------------------------
It appears that maybe the vendor's web presentation has changed/been modified recently. Hub Centric maybe moved one product to another but a knowledgeable purchaser should have questioned the specifications regardless. They certainly are though it seems 70.5 'Hub Centric' as advertised.

 

Except: The "original poster" DID more than consider a few other questions, and contacted the company (and several others) after the original post and got a reply that these would work with Stock rims and then again 2 days ago asking..... why the specs are now showing 70.5 when previously no center bore size was listed, (like in one of the other products)?? ... (That's why I verified in the first place)....The reply back was: "Corvette specs for wheel and hub are 70.3mm not 70.5". These will work for your application. I also sent them (not that it's needed), the year of car, year of rims and my 70.3mm measurements . I just reviewed the email again. Perhaps you may have verified it differently. Also: Other adapters didn't list the center bore at all. These ones NOW list 70.5mm in the description. So , no - not "what I ordered"

As a Side note: I also reached out to PE Motorwerks which came highly recommended as well. Guess what? Their spacers (with all Corvette years listed) are 70.5mm ! (Just got an email back from them TODAY that they WILL WORK !!!, ...... and in the same email: "The Corvette center bore is 70.3mm" !

I find it baffling how 2 manufacturers take the time to "inform me" that the hub bore of a Corvette is 70.3mm - which I already know /already referenced in my emails to them....... But their adapters are made with a 70.5mm center bore AND 70.5mm Hubcentric "Lip". ! (I just emailed them to find out what brand of "Magic dust" they use to make a 70.5mm lip fit into a 70.3mm Hole??? ) Seriously, I emailed to see how 70.5mm can fit into 70.3 mm... (Can't wait for the educated reply). To be fair, the PE Motorwerks adapters reference many other cars so while they should remove reference to the Corvette (at least when using factory rims) but, at least these are not being marketed only for corvettes. I'm guessing they are perfectly suitable for use with other cars, or possibly Corvettes with aftermarket rims. (But I'd be willing to bet that most quality aftermarket rims for a Corvette would also use the 70.3mm hub bore size. UPDATE: 3/27/21 2:15pm.... Response from PE Motorwerks Below:

UPDATE: 2:15pm Eastern Time today 3/27/21. From PE Motorworks one of the other manufacturers:

When asked about the 70.5mm spec:

<paste>

Hello,

We haven't had any issue from others about center bore size. However, if the item does not fit, we can send you a return label for sending the item back. 1987 Chevrolet Corvette has 5x120.65 bolt pattern, 12 x 1.5 thread size, and 70.3mm bore.
Looking forward to hearing from you.
-Pauline

Really ???? I find it impossible to believe that out of the thousands they've sold, not one corvette owner ran across this situation. The people they have responding to questions have no idea / understanding. But I guess that's the world we live in now. (Their last email stated that they've sold thousands. I'm guessing nobody using them on a corvette used stock rims).....

PS. This is the Ebay link they refer me to. The first cars listed on the fitment chart is the 2020 Corvette (and every other year). And.... the specs are listed at 70.5mm center bore! (Shoot me):


https://www.ebay.com/itm/-4-20mm-5x4...edirect=mobile

I can see where a manufacturer may see fit to make the hub bore / back portion of the spacer 70.5mm so it doesn't have issues fitting on the hubs of various cars, but how do any of these manufacturers expect a 70.5mm hubcentric lip to fit into a 70.3mm rim hub bore? Idiots / Non "car - people" , plain and simple......in a business that they should not be in. I've never used spacers / adapters (and I guess I know why now people have issues).

I agree with the other reply. Sending back. And not using any spacers. Not worth the risk.
PS. I'm guessing the recent change (70.5mm) in the mfg specs / corvette mods link above is due to my emails over the past week.

(Although, they still list for use with pretty much every year Corvette ever made)!

I'm wondering how many people actually bolted these on ?? The adapter just about fits into 1 set of my sawblades, I think they could be "forced on" since there is enough stud sticking through to thread on the lug nuts.. How many people may do this by mistake ??

Email response to me to my original questions:
<paste>

Hello,
We would like to thank you for taking an interest in our items.
1987 Chevrolet Corvette has 5x120.65 bolt pattern, 12 x 1.5 thread size, - 70.3mm bore.
The factory wheels you mention from 1984-1996 Chevrolet Corvette also has 5x120.65 bolt pattern 70.3mm bore.
These adapters will work with your car. 70.3mm center bore.

The back of your stock wheels have small cavities (at least 2" width and 1/4" deep) in the mounting pad for installation of these spacers. These cavities are NEEDED so that the lug nuts and wheel studs can sit in this pocket. Verify this before purchasing if using aftermarket rims.

The email response above makes it pretty clear to me that they are saying the adapters will work with stock rims and 70.3mm bore.